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SubjectRe: [RFC PATCH] tracing/kprobes: Avoid parsing symbol+offset when updating arguments
On Sat, 3 Nov 2018 13:43:16 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Sun, 4 Nov 2018 01:03:34 +0900
> Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
> > Introduce symbol_offset data structure for avoiding symbol+offset
> > parsing when updating arguments.
> >
> > For kprobe events, "@symbol+offset" is supported, that requires
> > to be updated when new module is loaded because @symbol address
> > can be solved at that point. Currently kprobe events saves
> > the "symbol+offset" string and parse it repeatedly, but that
> > is inefficient.
>
> Do we care if it's inefficient? It's only done on module load and at
> the beginning. That's far from a fast path.
>
> If anything, the original solution saves memory, which is a bigger
> concern than speed in this case.

OK, and original one saves lines too. Please drop it :)

Thank you,

>
> -- Steve
>
>
> > This introduces symbol_offset data structure which can save the
> > offset and symbol separated, so that we don't need to parse it
> > anymore.
> >
> > Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> > ---
> > kernel/trace/trace_probe.c | 49 +++++++++++++++++++++++++-------------------
> > kernel/trace/trace_probe.h | 7 +++++-
> > 2 files changed, 34 insertions(+), 22 deletions(-)
> >
> > diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
> > index bd30e9398d2a..0a3af7d6e133 100644
> > --- a/kernel/trace/trace_probe.c
> > +++ b/kernel/trace/trace_probe.c
> > @@ -201,6 +201,26 @@ static int parse_probe_vars(char *arg, const struct fetch_type *t,
> > return ret;
> > }
> >
> > +static struct symbol_offset *allocate_symbol_offset(char *sym_offs_str)
> > +{
> > + int ret;
> > + long offset = 0;
> > + struct symbol_offset *sof;
> > +
> > + ret = traceprobe_split_symbol_offset(sym_offs_str, &offset);
> > + if (ret)
> > + return ERR_PTR(ret);
> > +
> > + sof = kzalloc(sizeof(struct symbol_offset) + strlen(sym_offs_str) + 1,
> > + GFP_KERNEL);
> > + if (!sof)
> > + return ERR_PTR(-ENOMEM);
> > +
> > + sof->offset = offset;
> > + strcpy(sof->symbol, sym_offs_str);
> > + return sof;
> > +}
> > +
> > /* Recursive argument parser */
> > static int
> > parse_probe_arg(char *arg, const struct fetch_type *type,
> > @@ -253,9 +273,9 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
> >
> > /* Preserve symbol for updating */
> > code->op = FETCH_NOP_SYMBOL;
> > - code->data = kstrdup(arg + 1, GFP_KERNEL);
> > - if (!code->data)
> > - return -ENOMEM;
> > + code->symoffs = allocate_symbol_offset(arg + 1);
> > + if (IS_ERR(code->symoffs))
> > + return PTR_ERR(code->symoffs);
> > if (++code == end)
> > return -E2BIG;
> >
> > @@ -483,7 +503,7 @@ int traceprobe_parse_probe_arg(char *arg, ssize_t *size,
> > if (ret) {
> > for (code = tmp; code < tmp + FETCH_INSN_MAX; code++)
> > if (code->op == FETCH_NOP_SYMBOL)
> > - kfree(code->data);
> > + kfree(code->symoffs);
> > }
> > kfree(tmp);
> >
> > @@ -513,7 +533,7 @@ void traceprobe_free_probe_arg(struct probe_arg *arg)
> >
> > while (code && code->op != FETCH_OP_END) {
> > if (code->op == FETCH_NOP_SYMBOL)
> > - kfree(code->data);
> > + kfree(code->symoffs);
> > code++;
> > }
> > kfree(arg->code);
> > @@ -525,31 +545,18 @@ void traceprobe_free_probe_arg(struct probe_arg *arg)
> > int traceprobe_update_arg(struct probe_arg *arg)
> > {
> > struct fetch_insn *code = arg->code;
> > - long offset;
> > - char *tmp;
> > - char c;
> > - int ret = 0;
> >
> > while (code && code->op != FETCH_OP_END) {
> > if (code->op == FETCH_NOP_SYMBOL) {
> > if (code[1].op != FETCH_OP_IMM)
> > return -EINVAL;
> >
> > - tmp = strpbrk(code->data, "+-");
> > - if (tmp)
> > - c = *tmp;
> > - ret = traceprobe_split_symbol_offset(code->data,
> > - &offset);
> > - if (ret)
> > - return ret;
> > -
> > code[1].immediate =
> > - (unsigned long)kallsyms_lookup_name(code->data);
> > - if (tmp)
> > - *tmp = c;
> > + (unsigned long)kallsyms_lookup_name(
> > + code->symoffs->symbol);
> > if (!code[1].immediate)
> > return -ENOENT;
> > - code[1].immediate += offset;
> > + code[1].immediate += code->symoffs->offset;
> > }
> > code++;
> > }
> > diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
> > index 974afc1a3e73..942424d05427 100644
> > --- a/kernel/trace/trace_probe.h
> > +++ b/kernel/trace/trace_probe.h
> > @@ -103,6 +103,11 @@ enum fetch_op {
> > FETCH_NOP_SYMBOL, /* Unresolved Symbol holder */
> > };
> >
> > +struct symbol_offset {
> > + long offset;
> > + char symbol[];
> > +};
> > +
> > struct fetch_insn {
> > enum fetch_op op;
> > union {
> > @@ -117,7 +122,7 @@ struct fetch_insn {
> > unsigned char rshift;
> > };
> > unsigned long immediate;
> > - void *data;
> > + struct symbol_offset *symoffs;
> > };
> > };
> >
>


--
Masami Hiramatsu <mhiramat@kernel.org>

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